Hydraulic power tools are employed in numerous applications to provide a user with a desired mechanical advantage in a wide range of applications for pressing, forming, crimping, cutting, or otherwise manipulating one or more workpieces. One example application is in crimping tools used for making electrical connections, such as crimping a terminal to an end of a wire. Another example application is in cutting tools where hydraulic pressure provides force for cutting the workpiece.
Conventional hydraulic tools generally comprise a tool body, a fluid reservoir, a hydraulic pump, a cylinder defining a chamber, and a piston (i.e. ram) capable of being moved through a pressing stroke (i.e. advancing stroke) inside the chamber from a starting position to an advanced position under the effect of an injection of pressurized fluid into the chamber. These tools may comprise a variety of different working heads that can be removably attached to the body and which are adapted to being operated by the piston for manipulating the workpiece as desired.
Conventional tools generally comprise a manually operated fluid return valve, also referred to herein as a “control valve”, that when manually opened enables the pressure in the chamber to be reduced, whereby the fluid contained in the chamber is returned to the reservoir such that the piston is returned to a retracted position in the chamber with assistance from a spring or other biasing member. Typical fluid return valves are biased to be closed and are manually opened upon depressing a button or actuating lever for draining hydraulic fluid from the chamber. In certain tools, the button must be held in the depressed position to fully empty the chamber of hydraulic fluid and to fully retract the piston.
These tools also generally comprise an automatically operated pressure relief valve so that the pressure of the fluid injected into the chamber does not exceed a predetermined threshold. Pressure relief valves often comprise a movable needle closing a fluid escape opening and a spring holding the needle in the opening. The force exerted by the spring on the needle is calibrated so that the needle is automatically moved under the effect of the fluid pressure in the chamber only when the pressure reaches the predetermined threshold, referred to herein as the “set pressure” of the pressure relief valve, and closes when the pressure is below a predetermined threshold, referred to herein as the “reseating pressure” of the pressure relief valve.
Conventional electrically powered tools also typically comprise a switch for operating a motor, which drives the pump for pumping hydraulic fluid from the reservoir to the cylinder. The switch for the motor is turned on and off by use of a trigger or similar control means on most tools. The trigger for the motor is separate and distinct from the button for opening the return valve. This configuration thus requires separate manipulation of the trigger and the control valve button, wherein an operator has to depress the trigger to close the motor switch to operate the motor and separately depress the control valve button to drain hydraulic fluid from the cylinder.
Although satisfactory in many regards, known hydraulic power tools suffer from a variety of issues. Accordingly, a need remains for new hydraulic systems and tools using such systems.